how to work as fast as posible with pixels to make a transition betwen two images?
Not sure exactly what you're looking for, but I did create a cross-fading routine for blitzmax which can be found in the code Archives:
http://blitzbasic.com/codearcs/codearcs.php?code=1281
It will do a smooth fade from one image to another, as well as fade to black, and fade to white.
somewhat related, I also created this one:
http://blitzbasic.com/codearcs/codearcs.php?code=1282
Which fades a full color image into greyscale.